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Overview


FANS is an instrument used for neutron vibrational spectroscopy. Monochromatic neutrons of variable energy are inelastically scattered from the sample and detected at a fixed final energy Ef after they pass through a low-pass Bragg cutoff filter. Inelastic spectra are then recorded by scanning the incident energy and detecting all scattered neutrons with energy Ef < Ecutoff. With two different monochromators, FANS has an energy range of approximately 5 - 250 meV depending on the monochromator used:
Monochromator
Scan Energy Range
Pyrolytic Graphite [PG(002)] Without small shield: 2.5 meV ≤ E ≤ 25.0 meV
With small shield: 3.7 meV ≤ E ≤ 45.0 meV
Copper [Cu(220)] Without small shield: 25.0 meV ≤ E ≤ 175.0 meV
With small shield: 35.0 meV ≤ E ≤ 250.0 meV


Scanning the neutron energy requires moving a series of motors through various angles. Normally this is software controlled, but for reference here is a list of motor numbers and their descriptions. Traditionally, for triple-axis spectrometers, the motors are numbered "1" for the monochromator and increasing in order as the spectrometer is traversed. We are in the process of removing the triple-axis part of the spectrometer, so the numbering scheme is partly redundant.

MOTOR
HARDWARE
FUNCTION
Motor #1 Monochromator (θ) Moves the monochromator to satisfy the Bragg condition for the chosed neutron energy
Motor #2 Monochromator (2θ) Moves monochromator drum and sample table to the angle for the chosen incident energy
Motor #3 Sample table Rotates the sample
Motor #7 PG(002) monochromator focus Changes the vertical focus of the PG(002) monochromator
Motor #8 Cu(220) monochromator focus Changes the vertical focus of the Cu(220) monochromator
Motor #9 Filter/detector carriage Moves the filter carriage


Instrument scientists
Craig M. Brown (301) 975 5134
Terry Udovic (301) 975 6241
Juscelino Lećo (301) 975 8867

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Last modified 04-May-2004 by website owner: NCNR (attn: )